Mirador viewer

SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https://digital.libraries.psu.edu/iiif/info/maps1/27354/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-272b5c88-dc5e-45cf-8cd1-ffd3ee1bb968",
      "cw-4173cefa-585d-431c-9137-a3d9d949db87"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-73fc5960-b00f-4821-a648-984b73c160af",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/27354/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-4173cefa-585d-431c-9137-a3d9d949db87"
  }
}